Suppression of interference in carrier telegraph systems



Aprill, 1930. RR H. CLAPP 1,752,330

SUPPRESSION OF INTERFERENCE IN CARRIER TELEGRAPH SYSTEMS Filed Ndv, 15',1928 I [Ii 0251143441100 Receivin Cucuz I INVENTOR ATTORNEY g signalingchannel or' channels.

Patented Apr. 1, 1930 UNITED "STATES PATENT OFFICE I :BOBERT H. CLAYP,OF RAMSEY, NEW JERSEY, ASSIGNOB TO AMERICAN THEPHONE AND TELEGRAPHCOMPANY, A CORPORATION OF NEW YORK SUPPRESSION OF INTERFERENCE INCARRIER TELEGRAPH SYSTEMS Application filed November 15, 1928. SerialNo. 318,602.

produce, in response to the disturbance, an

impulse which tends to hold the armature of the receiving relay againstthe contact upon which it happens to rest at the instant of thedisturbance. This holding impulse is caused to flow through awinding ofthe receiving, relay, and in order that it may always be in such adirection as to hold the relay armature on its contact, a reversingarrangement is provided for reversing the direction of flow of currentthrough such winding as the signal changes frornmarking to spacing andvice versa.

The foregoing arrangementinvolves setting aside a frequency band for thebuck circuit which cannot be used for signaling. Fur= thcrrnore, inorder that the arrangement may be effective, the disturbance must occursimultaneously in the band assigned to the buck channel and the band orbands used for the I In accordance with the present invention, itis-proposed to overcome thesefilimitations byusing the samefrequencyjband both for signals and for the neutralizing impulse. Thisis accomplished by associating with each receiving rectifier of thesignaling channel an auxiliaryrectifier for producing, in response to adisturbance, a momentary impulse which will flow through a winding ofthe receiving relay in such direction as to oppose the effect of thedisturbing impulse in the relay during spacing and to assist therectified current suppliedby the receiving rectifier during marking. Theproper poling oftherneutralizing impulse may be accomplished as in thebuck signals corresponding to spacing. Experience shdws channel circuitby a suitable reversing arrangement. In order to prevent the auxiliaryrectifier from responding to marking signals, its grid is biasedsufiiciently ne tive so that its space current is substantialfi zerowhen normal marking signals are being receivedgf Withsuch anarrangement, 'no current will besupplied by the auxiliary rectifierduring the reception of waves of normal carrier frequency amplitudecorresponding to marking enduring the zero current interval that theinterfering disturbances are, for the most part,'of much greatermagnitude than the carrier current received during the marking interval.Consequently, when such-a dis turbance occurs it will cause current toflow in the auxiliary rectifier. This current is so poled by thereversing arran ,ihe'nt that it tends to hold the armature ofihereceiving relay upon either its marking or spacing contact depending uon the character of the signal ing receive" at the time of thedisturbance. v

The invention will now be more, fully understood from the followingdescription, when read in connection with the accompanying drawing, thefigure of which illustrates circuit arrangeemnt embodying theprinii'tples of the invention.

In the drawing, the apparatus of a single carrier channel only is shown,it being under stood, however, that other similar channels may beprovided in a multiplex system, either wire or wireless. The receivingchannel comprises the usual selectin circuit S, which may be atunedcircuit orja nd filter or other known device for selecting the bandassigned to the particular channel A reoeivingamplifier A is alsoprovided for amplifying-the received carrier waves, the plate circuit ofthis amplifier being supplied with current through the usual choke'coilL. The regular an operating winding 1 of the'receiving relay RR. Thereceiving relay also includes a biasing winding 3 through which a normalcurrent flows of such magnitude as. to produce a pull upon the armatureof the relay, tend ing to hold it against its spacing contact, this pullbeing about one-half as strong as that due to the rectified currentflowing through the winding 1 iii response to a marking signal; Thus,during spacing signals when no current flows in the circuit of therectifier D, the armature is held against the spacing contact, but whena train of carrier waves corresponding to a marking signal is re-'ceived, the rectified current flowing through the Winding 1 shifts thearmature to the marking contact.

In order to overcome the effects of disturbing impulses, an auxiliarydetector D is associated with the output of the amplifier A.

The grid is biased by means of a 0 battery CB which is connected betweenthe grid and the filament through a resistance 1". This resistance isprovided in order to. prevent the i low impedance of the grid batteryfrom act ing as a shunt with respect to waves transmitted fromthereceivingamplifier A. Such waves will be transmitted to the grid ofthe detector D through a capacity C which also serves to isolate thegrid of the detector D from the potential of the plate battery of theamplifier A. The grid battery CB is so arranged as to render the grid ofthe rectifier D more negative than the grid of the rectifier CB, sothat. no plate current will flow in the detector D until an applied waveis superimposed upon its grid with a magnitude greater than the normalcarrier waves received during the marking impulse. 'Consequently, thedetectorD produces no eifectduring the receipt of normal marking andspacing signals. As already stated, however, the disturbing waves areusually of greater amplitude than the normal signaling currents, andconsequently, whenever such a disturbing wave is received, a currentwill flow in the plate circuit of the rectifier D, as will be describedin more detail later. 'This plate current-flows through an auxiliarywinding-of the receiving relay RR'in a direction-determined by thecontacts of two polar reversing relays PR and PR. Thesereversing relaysare cone necte'd in the loop circuit which is controlled by thereceiving relay RR, and their arma cause the armatures of relays PR andPR to rest upon their lower contacts. If, with the circuit in thiscondition, an interfering disturbance should occur, such interferingwave, upon being impressed upon the grid of the detector D, will cause aplate current tofflow through the winding 1 of the receiving relay.Since the disturbing wave will usually be of much greater amplitude thana normal marking current, this impulse through the winding 1 will besllflicicnt, under normal conditions, to shift the armature of thereceiving relay to its marking contact. This action is prevented,however, by the fact that the disturbing wave is also applied to thegrid of the detector D, and

being of large amplitude it overcomes the normal negative potential ofthp grid D sufficiently 'to' cause a plate current to flow over thelower contact of the reversing relay PR through the winding 2 and thenceover the lower contact of the reversing relay PR. This current throughthe winding 2 is in such a direction as to oppose the current throughthe winding 1. It will also be sufficient to prevent the current throughthe winding 1 from shifting the armature, because the disturbing impulsewill usually be of sufl icient amplitude to overload the tube D andhence, the plate current of the tube D will not exceed its saturationvalue. Although a greater potential must be applied to the grid of thetube D in order tol iovercome 'its,norma1 bias, than need be applied tothe grid of the tube D, the actual potential applied is so great in bothcases that the plate current of the tube D will also be a saturationcurrent and hence, as great as the plate current of the tube D. Theeffect of the disturbing impulse is therefore neutralized duringthespacing condition. VVhen a marking signal is being received, carrierwaves are impressed upon the grids of the rectifiers D and D". Asalready stated,

the grid of the detector D.- is biased sufficient ly negative so thatunder these condition; no space current flows in the plate of thedetector D. In the case of the detector D, however,

which is biased negative to alesser degree, a rectified plate currentflows through the winding 1 of the receiving relay RR and shifts thearmatuneofthe receiving relay to its marking contact. The polar relaysPR and PR in the loop circuit thereupon shift their armatures to their uper contacts so that the plate of the detector 1 is connected to thewinding 2 of the receiving relay in such a manner as to cause currentfrom the plate (when flowing) to flow through the Winding 2 in theopposite direction to that described in connection with the spacingimpulse.

The effect of a disturbing impulse during marking is not always thesame. In some instances the disturbing impulse appears to have the cfiect of increasing the plate current in the rectifier D. This or course,has no at fect of producing fa se rfignal, and if a current is alsocaused. to flow in the plate circuit of the rectifier I) in It'xpullsQto such a disturhance such plate run/em will assist the plate currentfrom the rctifiei i to hold the armature against the marking contactuntil p the disturbance ceases. The H. .u arises in connection withdisturl m new i a t ypc that they cause a decree in the p re current ofthe detector 1), tliei feet of producing a fals While the cause of thisdc current is not fully understw i, ly due to the action of the r thecapacity C as a grid leula The disturbing impulse may tail e a highfrequency Wave within tte ass; tau selecting circuit S, the Wave ueia,great amplitude as to overcome ih -r negative bias of the grid of thedet'ccit drive the grid positive so that eienrni from the filament tothe grid. Div i negative clcmrons passing to the grit: c each positivehal f-Wave of the dist current magative charge is trapped up 4 grid Whit:1 quickly builds up, and by rend ing the id more negative tends toI'Htltl irar z-- ill. .7 r, :1 the amplitude of the disturb ivavc is nettoo great, so that the grid of it: rectifier Y (with its larger normalnega im bias} is actually driven positive durii iii-wave, a rectifiedcurrent ill 2. plate circuit of the rectifier D in response U thedisturbing impulse. This plate curres u may have a value equal to that,of the saturation condition of the tube, or th plate current may besmaller, depending upon the amplitude of the applied wave. In any event,the rectified current flows through the winding {tin such a direction toassist the late current;- of the rectifier D (it amp) and once, tends topnavent the false spacing signal due to the reduction of the plateCll'lffilll in the rectifier If the disturbing wave is of such amplitudeas to actually drive the grid 01" the tulicl) positiveso that the griddraws current from the filament, thereby trapping a negative charge uponthe grid due to the action of the condenser C and the resistance 1"acting as a i last i grid leak, the plate current of the rectifier D maybe less than its maximum or saturation value. Such plate current,however, will be in such a direction as to tend to h. hi the armafew innumber that the ouL; he Egwmi lt Wlll be obvious that tha w-ral pr spics herein disclosed may many other organization: from thoseillustrated .thnt from the spirit of the in in let: us: deli thefollowing claims.

\Vhat is claimed is:

1. In a carrier telegraph i can ii rcrewin; channel including a reel n gr52: t interns flu responsive to an intcrfciin; war: in said channel toproduce cur: in1g'--"u and means controlled b5 the irir g via. to applysaid current llaiplihh' t. w ll :vin as to tend to hold its urn a?against 83w if contict upon which it rm: u 2 im n: inu-rfcring Waveoer-um.

2. in a carrier telegraph w v ingf cha uel including a la.

us associated withsaid mi: 2 1 u naive to waves of now, i am l receivedin said chum-i I. c an ne rz ponsive to in rrl ez'in m'lhl mi-xl ofgreat-ia npliiuh r ral 3 warn to producia an @135 1 means to app!" -np st clayga'a as to ifl'i, fihilllt I J t t l pulse at. curpulse throughsaid auxiliary winding when signaling carrier waves are not beingreceived.

4. In a carrier telegraph system, a receiving channel including areceiving detector and a receiving relay, an auxiliary detectorassociated with said channel, said auxiliary detector being so biased asto be unresponsive to signal waves of normal amplitude received in saidchannel, but responsive to interfering waves of greater amplitude thannormal signal waves to produce a current pulse, and means to apply saidcurrent impulse to said relay so as to tend to hold its armature againstthe contact upon which it rests at the time the interfering wave occurs.

5. In a carrier telegraph system, a receiving channel including areceiving detector and a receiving relay, an auxiliary detectorcomprising a vacuum tube having grid, filament and plate electrodesassociated with said channel, said grid being so biased that no platecurrent will flow in response to normal signal waves but plate currentwill fiow in response to interfering waves of greater amplitude thannormal signal waves, and means to apply said plate current to said relayso as to tend to hold its armature against the contact upon which itrests at the time the interfering wave occurs.

6. In a carrier telegraph system, a receiving channel including areceiving relay, said relay having an operating winding, an auxiliarywinding, and means normally tending to bias the armature of said relayagainst one of its contacts, a receiving vacuum tube detector in saidchannel having its plate connected to supply operating current to saidoperating winding and its grid so biased that substantially no operatingcurrent will be supplied in the absence of received carrier waves, anauxiliary vacuum tube detector associated with said channel and havingits grid so biased that no plate current will flow in response tonormalcarrier signaling waves but plate current will flow in response tointerfering waves of greater amplitude than normal carrier signai waves,and means to cause the plate current from said auxiliary detector toflow through said auxiliary winding in such direction as to assist saidoper- 4 ating winding when carrier signal waves are vember, 1928.

being received and to reverse the direction of current flow through saidauxiliary winding when carrier signal waves are not being received. V

In testimony whereof, I have signed my name to this specification this14th day of No- ROBERT H. CLAPP.

